This program involves the study of regulation of the secretion of the hypophysiotropic hormones in man and in animals (hormonal feedback and neurotransmitter control), the mode of biosynthesis of the hypothalamic hormones, particularly TRH and LRH, histochemical localization of the releasing factors in relation to functional state of the animal, and the regulation of the pituitary thyroid axis. Also, we are concerned with the factors determining conversion of T4 to T3, and the tissue localization of these hormones.